Ion implantation is used to introduce atoms or molecules, generally referred to as dopants into a target substrate to change the material properties of the substrate. The technologies of Ion implantation are gaining particular interest because the ion implantation process is a process commonly used in making modern integrated circuits. Furthermore, ion implantation may also be used for thin film deposition with controlled thickness and predefined surface properties for manufacturing optical or display devices such as flat panel displays.
In certain applications it is advantageous to generate ion beams in the form of ribbon-shaped beams having high aspect ratios, particularly in the implantation of 300 or 450 mm wafers to generate a beam with the cross-section that is much larger in one dimension than the other. These ribbon beams are commonly used in ion implanter apparatus and implantation systems where a single workpiece such as a silicon wafer or flat panel display is moved in a single dimension through the ion beam. However, in order to reach a uniform dose of ions over the substrate the intensity of ribbon beam must be tuned to have a uniform intensity across the ribbon direction. The beam intensity uniformity is commonly obtained by moving some beamlets from higher intensity regions to regions that have lower intensity. For these reasons, the beam angle uniformity is sacrificed, which could be detrimental when applied in the fabrication processes of particular advanced integrated circuits. Specifically, when non-uniform beam incident angles relative to the wafers can generate large shadowing effect variations as the device dimension shrinks. The shadowing effects can cause non-uniform and insufficient dopants concentrations in some area on a wafer. Therefore, the non-uniform beam incident angles produce different shadowing effects thus cause the poor dopant uniformity on the wafer that leads to reduced production yields due to the ion implant deviations. For these reasons, there is an urgent need to improve the implant angle uniformity. These problems and difficulties are further explained below in FIGS. 1 to 3.
FIG. 1 is a perspective view of a ribbon-beam system according to the prior arts in which the ion beam diverges through an analyzer magnet and is then collimated by a lens. The beam is expanded through the AMU magnet to form a ribbon shape beam. The collimator corrected the beam divergent angles. However, this system needs a device to manipulate beam intensity so that beam can be uniformed. It is not an easy task to develop a device and beam intensity control algorithm to provide a uniform beam. The most problematic issue is that the beam angle uniformity has to be sacrificed for beam intensity uniformity since beamlets are moved from higher intensity regions to lower regions. These beamlet moves are accomplished by changing beamlet angles.
FIG. 2 depicts another conventional ion implantation system that generates a narrow beam taller than the target. The beam current is tuned to uniformity by a multipole magnet 402 and multipole magnet 404. The multipoles move some parts of the beam from a position (high intensity) to another position (low intensity) in divergent direction, i.e., a vertical direction as shown in the figure. But the movement of the beam causes the non-uniformity in the implant angles. Different parts of the beam will have different incident angle towards wafers as shown in FIG. 2A.
FIG. 3 depicts another implant system that generates a spot beam smaller than the target. The beam height is smaller than wafer diameter, 2D mechanical scans (a wafer is held on a robot type of object that can move left/right and up/down to form beam implanted pattern as shown FIG. 3A. In order to have sufficiently good implanted dose uniformity, the implant process requires multiple scan operations. The implant process thus requires longer scanning time. Also, there are many turns around on left and right ends and these turns around that have decelerations and accelerations must happen when beams are not in wafers so that beams are wasted. The implant system utilizes a spot beam small than the target thus has poor beam utilization.
As discussed above, due to the complex interactions between the ion beam and the magnetic field applied for beam expansion, this approach creates severe technical, practical, and process related problems that increase the total production cost of such equipment and lead to more complicated operation procedures for carrying out the ion implantation. In particular, the beam path through this system is relatively long, and at low energies and high beam currents it becomes increasingly difficult to control the uniformity of the ion beam and the angular variation within the beam with the precision required by certain commercial processes.
It is further desirable to generate implanting ions with an ion current of milli-amperes and at an energy level as low as 200 ev. The highest beam currents are obtained by decelerating the ion beam immediately prior to the target. However this practice has several known disadvantages. One disadvantage is that the deceleration tends to modify the trajectories, magnifying any angular errors and making it very difficult to control both the angle and dose uniformities in a scanned ion beam.
Since the conventional types of ion implantation systems cannot provide a viable solution for performing one wafer at a time implantation with a high-current, high dose and angle uniformities there is a need in the art of integrated circuit fabrication to provide a new system to resolve the above-discussed difficulties. A new system configuration is required to generate a high current implantation with improved dose uniformity without sacrificing the implantation angle uniformity while reducing the production cost and simplifying the manufacturing processes.